Superconductivity and magnetism in tantalum graphite multilayers based on natural graphite

DC magnetization and AC magnetic susceptibility of Ta-graphite (Ta-G) based on natural graphite (NG) have been measured using a SQUID magnetometer. In this system, Ta multilayers sandwiched between adjacent graphite layers would be periodically stacked along the c axis. Each Ta layer is composed of Ta nanoparticles in the form of either one-dimensional chains or two-dimensional platelets. An irreversible effect of magnetization is observed around 10 K, suggesting the occurrence of a spin-glass like behavior reflecting the frustrated nature of Ta nanoparticles as localized spins. A Meissner-like behavior is also observed below 10 K. The superconducting property of Ta-G (NG) is similar to that of tantalum carbide (TaC) nanoparticles based on carbon nanotubes, suggesting the existence of TaC nanoparticles in Ta-G (NG) as a minority phase.